Part 1: Design

Section D: Spinning to a Standard

Discuss how to determine the amount of twist per inch/centimeter and its relation to twist angle.

There are several ways to determine the number of twists per unit of length. They vary in accuracy and ease of use and those that are more accurate in theory are considerably less practical in practice. In all cases, each method can only measure the specific section of yarn being tested and multiple samples will give a better picture of the overall answer. Methods of interest to handspinners are described below.

Counting treadles

Each rotation of the drive wheel on a spinning wheel creates a certain number of twists in the yarn because the ratio of the diameter of the drive wheel to the flyer or bobbin whorl is fixed. This can be used to estimate the twist inserted into the yarn by counting rotations or treadle cycles (of both treadles for a double treadle wheel, because each contributes only half a rotation.) For example, if a certain yarn is spun with a 6:1 ratio and 5 treadle cycles while drafting 30 cm, then the yarn has 6 times 5 divided by 30 or 1 twist per centimeter.

Self-ply

A freshly spun single will twist back on itself to form a two-ply yarn with approximately half the twist of the single. Pull a length of yarn off the bobbin (to get a fully-formed yarn) and let it twist back on itself. Count the number of twists per centimeter or inch and multiply by two. Untwist to continue spinning without breaking off the yarn.

Counting fibers

For larger yarns, it is possible to trace the path of a fiber and determine how many times it wraps around. Mark a few fibers with a water-based dye or pen to make them easier to see.

Untwisting

A length of yarn can be manually untwisted to determine the number of twists. Measure the yarn and hold it under tension while you count the number of rotations it takes to completely remove the twist. A tensioned box such as the one described in The Alden Amos Big Book of Handspinning will help.

Twist angle is the apparent angle of the twisted fibers in the yarn. Measure it with a protractor or a specially marked chart and the axis of the yarn as zero. A small angle is a less twisted yarn and a large angle is more. It can be very difficult to measure the angle of twist for small yarns. There is a trigonometric relationship between the twist angle and twists per unit length based on the diameter and the length of one rotation of the yarn. It is only as accurate as one's measurements of twist angle, twists per unit length and diameter and one's interest in engaging in mathematical theory.

An extensive discussion of twist, twist angle, and twist measurement can be found in Physical Testing of Textiles by B. P. Saville.

Notes

Maximum 12 points

Examiner 1: 12

Examiner 2: 12

Examiner 1 approved of the "mathematical theory" comment, something I included because I think that sometimes people get too worked up about measuring twist. The entire concept of measuring twist is a product of industrial textile production, where it is yet another knob on the machine. It is impossible to do any sort of counting of rotations on a spindle and I completely cannot see an ancient spinner tracing fibers or unwinding yarn to measure the twist. It is either hard or soft, and fairly consistant results can be had by little more than practiced observation.